I checked everyone's dietary restrictions beforehand. I served fake meat without informing them at my wife's request, because she knew her father (who is stubborn southerner) and brother (who is mentally handicapped) would both refuse to like it immediately. (A visit to an all-vegetarian restaurant would later prove her correct).
In all other circumstances where I've served fake meat to others it's been very openly labeled and/or pointed out.
I'm inclined to agree with everything you've said, but Thanksgiving with the in-laws is a special moral situation, vegetarian or not :)
Secretly serving non-vegetarians vegetarian food is, technically, fraud, but it's not disrespecting their morality. That fraud might be slightly immoral (I don't think it is, but it's a topic for debate), but it's easily offset by the potential for convincing someone to become vegetarian.
* I think it was absolutely unethical of me. But it's one of those unethical things you do with in-laws, and falls within "white lies" territory as long as am I'm not endangering anyone's health nor causing them to violate moral principles.
* It was done simply to serve food we'd all eat, it was not my goal nor intention to "convert" anyone. Personally, I don't try to convert people beyond example and offering my reasonings when socially appropriate.
* I would consider tricking me into eating meat as worse than tricking someone to eat more non-meat than they would. That doesn't make what I did less of a trick.
People may be eating what they choose to eat with just as much moral conviction as your vegetarianism. That is not for you to decide.
You have no right to deceive others about what they are putting into their body, let alone in hopes of "convincing" or converting them.
You have no right to physically force your own morality upon others without their informed consent.
Think about what you have just argued for here.
On top of that, it's very likely that every ingredient in the "turkey loaf" was something that would not be out of place in an actual turkey loaf. In other words, no ingredients being secretly added, just one being removed.
So again here there is a difference adding a problem ingredient, and there being an ingredient you don't put in. For the former you need to ask about dietary restrictions and respect that. Which they did. For the latter, I don't think you're in much risk of violating anyone's moral system.
If it's unrelated to GMOs, I'm genuinely interested in what your objection might be.
Most people don't do that. It seems reasonable to assume (until established otherwise) that his inlaws have not done that.
Wouldn't you be upset if your in-laws served you seitan that was actually chicken?
*edit: I bring this up because many people do not react well to meat substitutes. Gluten and soy intolerance affects many people and serving soy or gluten-based meat substitutes without prior informed consent can induce adverse reactions. I do believe that veganism in morally superior to carnivorism, but that still doesn't grant the right to trick others into consuming meat substitutes without their informed consent.